There are a wide variety of optical sorting systems which have been described in the prior art for sorting objects such as beans, grains, fruit and the like based on color and/or size. These systems are similar in that they have a feeding device for feeding the objects which also serve to separate the objects from each other. As the objects move into an analysis area they are illuminated and the light which is reflected from the objects is detected by one or more light detectors. If the analysis is to be based either in whole or in part on color there would be at least two detectors whose response characteristics, as a function of frequency, would be different. The detectors produce electrical signals which are related to the light which they detect and these electrical signals are then processed by electronic circuitry which gives an indication as to whether or not the object is acceptable. This signal is provided to a deflecting device which will deflect the object depending upon the signals received from the processing circuit.
Although a variety of systems of the type generally outlined above are available and described in the prior art a number of problems have not been solved and our invention is addressed to these problems. In particular, since the comparison system employs light detectors with differing response characteristics two light signals must be developed, one for each detector. In order that the analysis operate solely as a function of the light reflected from the object the two light signals should comprise only reflected light and should, furthermore, be identical. Prior art systems have employed complicated systems of lenses and dividing mirrors to perform this function which are not wholly satisfactory from the standpoint of cost and accuracy. It is also preferable to derive the reflected light from the entire surface of the object. Some prior art systems have had difficulty in obtaining reflected light from all or a majority of the surface of the object being analyzed.
A majority of the prior art systems of which we are aware determine acceptability of an object based upon color alone. That is, each of the nominally identical light signals is directed at a photodetector whose response characteristics peaks in different areas of the light spectrum. In this way, the output signal from each detector is indicative of the reflectance of the object at the wave lengths which the detectors output peaks. By comparing these signals; usually the ratio is determined, a quanity is developed which is characteristic of the object's color. By establishing predetermined limits only objects with nominally proper colors will be accepted, and others will be reflected. One difficulty with this approach is that object size is another factor which should be taken into account in determining whether it is acceptable or not. Clearly, signals which have been derived as is described above do not contain information relating to the size of the object and therefor will not serve to select objects only within predetermined size limits.
Since the analysis, which has been briefly described above, is based on light reflected from the object in an analysis zone, it is apparent that the analysis apparatus should operate only during the period when the object is illuminated. This synchronization function has, however, proved to be difficult when a number of analysis criteria are being employed. Thus, some prior art systems sense the object at a location preceding the analysis zone and enable the analysis apparatus a predetermined period after the object is sensed. For objects of nominal size which travel from the sensing location to the analysis zone in a nominal period of time the system, of course, works quite well. However, when objects vary in size and/or travel with variable speeds between the sensing location and the analysis zone difficulties occur in that the analysis circuitry is operating when the object is not correctly positioned. This, of course, leads to anamalous signals and may lead to erroneous operation.
Furthermore some systems, which rely solely on instantaneous reflected light, may be subject to erratic operation as a result of the complex nature of the signals.